For providers who deliver bitstreams containing content data, such as moving image streams and audio streams, if the efficiency of network resources can be enhanced, it will be advantageous in reducing operational costs. There is therefore a need to reduce the file size of data to be delivered, by converting already compressed bitstreams into bitstreams encoded by a higher-efficiency encoding scheme.
From a user's side there is also a need for converting a large-capacity video stream into a video stream of a smaller file size so that the video stream can be easily previewed on an existing network having a limited transmission band.
FIGS. 1A and 1B are diagrams each depicting a prior art process for converting a bitstream encoded in a given format (scheme A) into a bitstream of a different format (scheme B). The process depicted in FIG. 1A performs the conversion by using a decoder of scheme A, which converts the bitstream of scheme A back into the original data, in combination of an encoder of scheme B which converts the original data into the bitstream of scheme B, while the process depicted in FIG. 1B converts the bitstream of scheme A directly into the bitstream of scheme B. In either case, the conversion process is not performed in a parallel fashion, but performed continuously starting from the beginning of the bitstream and working through to the end thereof.
The bitstream format is defined by using various elements. For example, when the bitstream contains a moving image stream, the bitstream format is defined, for example, by the encoding scheme used to encode the moving image stream, the bit rate and frame rate of the stream or the size of the moving image, etc. On the other hand, when the bitstream contains an audio stream, for example, the bitstream format is defined by the encoding scheme used to encode the audio stream, the bit rate and frame rate of the stream, etc.
Patent document 1 listed below discloses a video encoding method and apparatus that can encode video scene data efficiently in a parallel fashion.
Patent document 2 listed below discloses an image encoding and decoding method which, when an image is encoded after it is split into a plurality of screen images, can prevent boundaries from becoming noticeable in the reconstructed image.
Patent document 3 listed below discloses a moving image encoding apparatus that can encode a moving image signal with high efficiency while preventing image degradation even when the moving image signal is encoded after it is divided it into a plurality of screen images.
Patent document 4 listed below discloses a method for using the slice structure used in video encoding in order to encode and decode a part of video redundantly.
Patent document 5 listed below discloses a multimedia conversion system that converts only the difference between the section the user specified from among multimedia data and the already converted section of the multimedia data and combines it with the already converted multimedia data for delivery to the user.
Patent document 6 listed below discloses an encoding method that makes it possible to reproduce an image smoothly even when a plurality of separately encoded bitstreams are decoded successively.
Patent document 7 listed below discloses a video/audio signal editing apparatus which, when trimming an MPEG-2PS stream, generates data containing sequence-end information that follows the data immediately preceding the deletion start position, generates data containing sequence-start information at the position immediately preceding the data that follows the deletion end position, and updates the file management information so that the generated data are contiguous with each other.
Patent document 8 listed below discloses a distributed parallel transcoder system, which limits the connecting point of a plurality of split image data to a scene change point.    Patent document 1: Japanese Unexamined Patent Publication No. 2002-199392    Patent document 2: Japanese Unexamined Patent Publication No. H09-284756    Patent document 3: Japanese Unexamined Patent Publication No. H05-183891    Patent document 4: Japanese Unexamined Patent Publication No. 2004-236337    Patent document 5: Japanese Unexamined Patent Publication No. 2006-352443    Patent document 6: International Publication Pamphlet No. 97/13367    Patent document 7: Japanese Unexamined Patent Publication No. 2005-33382    Patent document 8: Japanese Unexamined Patent Publication No. 2005-176069